The chief of the EU's monitoring mission said Sudan had "not reached all [standards] but some of them".
The polls were intended to effect a democratic transformation in Africa's largest country.

The complicated ballot has already been heavily criticised by the Sudanese opposition and local observers. Final results are expected on Tuesday.

The EU's team was withdrawn from Darfur, where a low-level civil war continues, because of fears about safety and whether the monitors could observe freely.

Final results of the presidential and legislative ballots are due on Tuesday, and President Omar Hassan al-Bashir is widely expected to win, most of his rivals having boycotted the proceedings, accusing him of vote rigging.

"It is apparent that the elections will fall short of meeting international standards and Sudan's obligations for genuine elections in many respects," said a statement from the U.S. Carter Center seen by Reuters.

The preliminary statements will be a blow to Bashir who, analysts say, is looking for an internationally recognised win to legitimise his rule and fend off International Criminal Court charges that he masterminded war crimes in Sudan's western Darfur region.

The elections were set up under a 2005 peace deal that ended more than two decades of north-south war in the oil producing state and also promised southerners a 2011 referendum on whether they should split off and become an independent country.